1. Field of the Invention
The present invention relates to a charging device used in an image forming apparatuses, such as a copying machine, a printer, or a facsimile.
2. Description of the Related Art
In an electrophotographic image forming apparatus, a toner image is formed on a charged photosensitive member. An example of a device charging the photosensitive member is a corona charger using corona discharge. Since the corona charger utilizes corona discharge to charge the photosensitive member, the charger generates discharge products, such as ozone (O3) and nitrogen oxides (NOx).
When the discharge products generated by corona discharge adhere to the photosensitive member, the products absorb moisture in the air, thus reducing the surface resistivity. In particular, in a high humidity environment, an electrostatic latent image based on image information cannot be faithfully formed in a portion to which the discharge products have adhered (such a problem is called “image deletion”).
Patent Literature 1 discloses a configuration in which an opening of a corona charger is covered with and closed by a shutter in order to prevent discharge products from depositing on a photosensitive member during non-image formation. Specifically, the configuration in which the shutter is moved so as to be opened or closed in the longitudinal direction of the corona charger is disclosed. To prevent “image deletion”, there are a method of heating the photosensitive member to prevent discharge products from absorbing moisture and a method of polishing the photosensitive member to remove discharge products. As compared to these methods, the configuration in which the shutter is provided for the corona charger has advantages in that energy required for heating is reduced (energy conservation) and the amount of polishing the photosensitive member is reduced to extend the life of the photosensitive member.